Three-step plasma treatment of copper foils to enhance their laminate adhesion

ABSTRACT

A three-step plasma treatment for improving the laminate adhesion of metallic and non-metallic substrates is described. The treatment comprises sequentially exposing the substrate to a first plasma of oxygen gas, a second plasma of a hydrocarbon monomer gas and a third plasma of oxygen gas. The process has particular utility in forming polymeric films on one or more surfaces of copper or copper alloy foils to be used in printed circuit applications.

This application is a division, of application Ser. No. 554,466, filedNov. 22, 1983, now U.S. Pat. No. 4,524,089.

This application is related to co-pending U.S. patent application Ser.No. 554,465, filed on Nov. 22, 1983, to Haque et al. for a ONE-STEPPLASMA TREATMENT OF COPPER FOILS TO INCREASE THEIR LAMINATE ADHESION,now U.S. Pat. No. 4,526,806.

This application is directed to the production of treated copper foilfor use in electronic devices.

Printed circuit boards are currently used as the substrate materials ina wide variety of electronic devices. Typically, these boards arefabricated from a thin sheet of copper foil laminated to either afiberglass/epoxy hardboard or, in some cases, flexible plasticsubstrates. During the latter stages of fabrication, the majority of thecopper foil is etched away to provide the desired interconnectingcircuitry between various components in an electronics circuit design.With improvements in etching technology, it is currently possible toachieve intercircuit line spacing approaching 3 to 5 mils. Minimum linespacing is one of the current technical limitations to continuedminiaturization of complex circuits. As the minimum line spacing isreduced, a higher density component packing is permitted on a circuitboard. Attempts to further reduce the minimum line spacing have becomelimited by the physical characteristics of the copper foil.

Generally, copper foil is produced by either electrodeposition or arolling technique. In both cases, the resultant surface of the foil isnot readily amenable to producing adequate bond strength afterlamination. As a result, all foil must be treated by an additionalelectrochemical process to improve its bondability. The most commonelectrolytic techniques currently used to improve the adhesion of copperfoils are directed to the production of dendritic surfaces on the copperfoil. The dendritic surfaces improve adhesion by contributing tomechanical interlocking between the copper foil and the substrate.However, the dendritic or roughened surfaces can for specificapplications unfavorably affect the performance characteristics of thefoil. For example, line spacing in the selective etching of copper foilscould be adversely affected. Further, the degree of attenuation and thespeed of transmission of high frequency signals could also be adverselyaffected. In view of this, a treatment that yields a copper foil withimproved adhesion without increasing the overall surface roughness ismost desirable.

Some interest in using substrates having polymer film coatings forprinted circuit applications has been expressed in the prior art.Polymer coatings are particularly advantageous because they can serve ascapacitor dielectrics, insulators, and/or protective layers. A varietyof different approaches including sputtering and ion implantation havebeen tried in an attempt to coat various metallic and non-metallicsubstrate materials with polymer films. U.S. Pat. Nos. 3,703,585 toAgnone et al. and 4,264,642 to Ferra illustrate some of these differentapproaches.

The technique for forming polymer films that has drawn the mostattention is the glow discharge plasma technique. It has been found thatpolymer films formed using this technique have unique physicalproperties and are relatively thin and substantially pinhole-free. Mostglow discharge plasma treatment techniques consist of placing asubstrate to be coated in a plasma in a surrounding chamber andinjecting a particular gas such as a monomer into the chamber. The typeof gas injected into the chamber normally depends upon the type ofpolymer coating to be deposited on the substrate. U.S. Pat. Nos.3,518,108 to Heiss, Jr. et al., 4,013,532 to Cormia et al., 4,133,691 toMorley et al., 4,166,784 to Chapin et al., 4,170,662 to Weiss et al. and4,226,896 to Coburn et al. and the article "A Review of Recent Advancesin Plasma Polymerization" by Mitchel Shen et al., Plasma Polymerlzation,American Chemical Society, 1979 illustrate some of the plasmapolymerization treatments that have been used in the prior art.

While most glow discharge treatments inject a single gas into thechamber in which the plasma is formed, it is also known to deposit apolymer coating on a substrate by placing the substrate in a plasmacontaining a mixture of gases. In U.S. Pat. No. 3,940,506 to Heinecke, aprocess is described for selectively treating a surface of an articlecomprising silicon in part and either silica or silicon nitride in partby placing the article in a plasma containing fluorine, carbon and areducing species such as trifluoromethane to deposit a fluoropolymercoating on the article.

In yet another glow discharge plasma treatment process, an amorphouscontinuous layer of SiO_(x) is deposited onto a substrate in a series ofthin layers by glow discharge of an organosilane and oxygen,interrupting the deposition as required, and initiating a glow dischargein oxygen after each interruption and prior to each subsequentdeposition. U.S. Pat. No. 4,260,647 to Wang et al. illustrates this typeof approach.

In accordance with the present invention, a three-step plasma treatmentfor depositing a polymer coating on a substrate material to enhance itslaminate adhesion is provided. The treatment comprises sequentiallyexposing a substrate material to be coated to a plasma of oxygen, aplasma of hydrocarbon monomer, and a second plasma of oxygen. While theprocess of the present invention has wide applicability, it has beenfound to have particular utility in depositing relatively smoothpolymeric films on copper and copper alloy foils.

The process of the present invention is preferably performed byinserting the substrate material to be coated into a chamber containingtwo electrodes. The chamber is first evacuated to a desired basepressure. After evacuation to the base pressure has been completed,oxygen in gaseous form is introduced into the chamber at a desired flowrate and the system is adjusted to a desired working pressure. Asuitable current at a desired frequency and a desired power level areapplied to the electrodes to create a plasma of oxygen. After thesubstrate has been exposed to the plasma for a desired time, the poweris turned off, the gas flow is shut off, and the chamber is evacuatedback to the base pressure. After the chamber has stabilized at the basepressure, a second gas such as a hydrocarbon monomer is introduced intothe chamber at a desired flow rate and the system is adjusted to thedesired working pressure. A plasma with the second gas is then createdby applying current and power to the electrodes. Again, after thesubstrate has been exposed to the second plasma for a desired period oftime, the power is turned off, the second gas flow is shut off, and thechamber is evacuated back to the base pressure. Thereafter, thesubstrate undergoes a third step wherein oxygen is again introduced intothe chamber at a desired flow rate and the system is again adjusted to adesired working pressure and a plasma is created.

It is believed that during the first step or oxygen pretreatment, thesubstrate material is primarily being cleaned. For example, where thesubstrate material comprises a copper foil, residual hydrocarbons,greasy materials and/or other contaminants are believed to be removedfrom the surface on which the coating is to be deposited. There may alsobe during this step some oxide formation on the surface of thesubstrate. The second step deposits the polymer film onto the substratesurface. It is believed that during the third step or oxygenpost-treatment some of the bonds in the series forming the polymer filmreact with the oxygen to provide polar bonding sites for improvedadhesion effect.

The process of the present invention may be performed in a singlechamber in a batchwise manner or may be performed in a plurality ofchambers in a continuous or semi-continuous manner. After the three-steptreatment has been completed, the polymer coated substrate material maybe laminated to another material. For example, the polymer coatedsubstrate may be laminated to a fiberglass epoxy substrate in the caseof printed circuit boards or to a polyimide in the case of flexiblecircuits.

It is an object of the present invention to provide a process fortreating a substrate material to improve its bondability.

It is a further object of the present invention to provide a process asabove for forming an adhesive polymeric coating on one or more surfacesof a substrate material.

It is still a further object of the present invention to provide aprocess as above for treating metal foil such as copper foil with apolymer coating to improve its laminate adhesion.

These and other objects will become apparent from the followingdescription and drawings in which like reference numerals designate likeelements.

FIG. 1 is a schematic illustration of an apparatus that can be used toperform the process of the present invention.

FIG. 2 is an exploded view of a portion of the apparatus of FIG. 1.

In accordance with the present invention, a process for depositing apolymer film on at least one surface of a substrate material forimproving the laminate adhesion of the substrate material is provided.While the following description describes the invention in the contextof forming a polymer film on copper foil, the process of the presentinvention has wide applicability in treating other metal and metal alloysubstrates as well as treating non-metallic substrates. Furthermore,while the invention will be described as a batch operation, it can beused as part of a continuous or semi-continuous operation.

Referring now to the Figures, the apparatus 10 includes a vacuum chamber12 in which the polymerization of the substrate material 14 takes place.In the vacuum chamber are two electrodes 16 and 18, generally an anode16 and a cathode 18. The electrodes 16 and 18 are both connected to anexternal power source 20 which may be either any conventional DC sourceor any conventional AC source known in the art. An AC source ispreferred because films deposited from DC glow discharge systems aregenerally poor and difficult to reproduce. The electrodes 16 and 18 canbe a screen, coil or plate formed from any suitable electrical conductorsuch as stainless steel, platinum or graphite. When an AC power sourceis used, the electrodes 16 and 18 may also be formed from dielectricmaterials.

In using an AC power supply, a current at a desired frequency and adesired power level is supplied to the electrodes. Both the frequencyand the power level can be varied over a broad range as is well known tothose skilled in the art.

If desired, the anode 16 may be adjustable. Suitable means 22 foradjusting the position of the anode relative to the cathode may beprovided. There may also be an indicator 24 for displaying theseparation between the anode and cathode. Generally, the electrodes 16and 18 are spaced from about 2" to about 6" apart. In those situationswhere the frequency is other than a radio frequency, one or more magnetsnot shown may be mounted on the electrodes 16 and 18 to enhance theplasma.

The chamber 12 has an outlet 26 which permits evacuation of the interiorof the chamber. The outlet 26 may be connected to any suitableconventional vacuum pump system (not shown) known in the art forevacuating the chamber 12 to a desired base pressure.

The chamber 12 also has means 28 for introducing a gas or a mixture ofgases into the chamber interior. The gas supply means 28 may compriseany suitable means known in the art such as a gas distribution ring orone or more conduits opening into the chamber interior. The gas supplymeans 28 may be connected through a suitable ducting and valvearrangement to one or more gas sources such as one or more gascontainers not shown. If a plurality of gas conduits are used in lieu ofa gas distribution ring, each gas conduit can be connected to anindividual gas source. Any suitable valve arrangement sufficient topermit regulation of the mass and/or volume flow rate of each gasflowing into the chamber interior may be provided as part of the gassupply means. If desired, a pressure indicating device not shown such asa manometer may be used to indicate the pressure level inside thechamber.

If desired, the chamber 12 may also be provided with means 29 forheating the interior and/or means 30 for cooling the interior. Theheating means 29 may comprise any suitable means known in the art suchas a resistance coil. The cooling means 30 may also comprise anysuitable means known in the art such as a water cooling loop. If needed,means not shown for independently heating the substrate material to becoated and/or either electrode 16 and 18 may also be provided.

In performing the process of the present invention, the substratematerial 14 to be coated can be placed in one of a plurality ofpositions. For example, it may be grounded to the anode, grounded to thecathode or placed in the plasma in an ungrounded condition. In apreferred technique for performing the process of the instant invention,the substrate 14 is placed ungrounded between the electrodes 16 and 18.Any suitable means known in the art may be used to position thesubstrate 14 in the desired location. Prior to being placed in thechamber 12, the substrate material may be cleaned using any suitablecleaning treatment known in the art. Of course, the type of cleaningtreatment used will depend upon the nature of the material forming thesubstrate and the type of contaminants on the material.

The process is commenced by evacuating the chamber 12 to a desired basepressure. It has been found that evacuating the chamber to an initialpressure in the range of about 10⁻⁵ Torr to about 10⁻⁶ Torr isdesirable. After the initial vacuum has been established, oxygen isintroduced into the chamber through the gas supply means 28 at a flowrate in the range of about 0.5 standard cubic centimeters per minute,hereinafter sccm, to about 50 sccm, preferably from about 5 sccm toabout 10 sccm. The oxygen gas is introduced into the chamber interior ata desired working pressure level which is not so low that there is aloss of discharge and not so high that electrical instability and arcingoccur. It is desirable to have the pressure in the range of about 5millitorr to about 100 millitorr, preferably from about 10 millitorr toabout 50 millitorr. After the oxygen gas has been introduced into thechamber 12, electrical power and current are supplied to the electrodes16 and 18 by the external power source 20. Since the power level neededto achieve the desired deposition characteristics appears to bedependent upon the geometry of the deposition equipment, it appears tobe meaningful to describe the power in terms of power per electrode area(watts/in²) and/or power per contained plasma volume (watts/in³). Theprocess of the present invention may be carried out using a level ofpower per electrode area in the range of about 1.00 watt/in² to about14.8 watts/in² and/or a level of power per contained plasma volume inthe range of about 0.17 watts/in³ to about 2.65 watts/in³. Preferably,the level of power per electrode area is in the range of about 4.9watts/in² to about 10 watts/in² and/or the level of power per containedplasma volume in the range of about 0.88 watts/in³ to about 1.75watts/in³. The current to the electrodes 16 and 18 is preferablysupplied at a frequency in the range of 10 kilohertz to about 20gigahertz. Most preferably, the current frequency is within the range ofradio frequencies and is from about 1 megahertz to about 100 megahertz.A frequency of about 13.56 MHz has been found to be particularly useful.The power being supplied to the electrodes 16 and 18 and the gasintroduced into the chamber 12 create a plasma in the chamber 12.

The substrate 14 is exposed to the plasma of oxygen for a desired timeperiod. It has been found to be desirable to expose the substrate duringthis first step to the oxygen plasma for a time period in the range ofat least about 5 minutes to about 40 minutes, preferably from about 10minutes to about 20 minutes. It is believed that during this oxygenpretreatment step, each surface of the substrate 14 that is to be coatedis being cleaned. For example, where the substrate 14 comprises copperfoil, residual hydrocarbons, greasy materials and/or other contaminantsare believed to be removed from the exposed surface or surfaces of thecopper foil. While the substrate material is generally cleaned prior tobeing placed in the chamber 12, this pretreatment step is believed toremove some, if not all, residual contaminants. There is also believedto be during this step some oxide formation on the exposed surface orsurfaces. However, these oxides are not believed to be detrimental tothe process as a whole.

After the substrate 14 has been exposed to the plasma for the desiredtime period, the power is turned off, the oxygen flow is stopped and thechamber 12 is evacuated back to the desired base pressure. After thechamber has stabilized at the base pressure for a desired period oftime, a second gas is introduced through the gas supply means 28 intothe chamber 12. The second gas is introduced at about the same flow rateand under the same working pressure conditions as the oxygen in thepretreatment step. The second gas may comprise any suitable monomer forproducing a desired polymeric film. When copper foil is being treated,it has been found to be useful to introduce a hydrocarbon monomer intothe chamber 12. For example, the second gas may be either methane,propene, or butadiene. After the second gas has been introduced into thechamber under the desired pressure conditions, the power is turned on asin the first step and a plasma is again created. It has been founddesirable to expose the substrate 14 to the monomer gas plasma for atime period in the range of about 0.5 minutes to about 10 minutes, mostpreferably from about 2.5 minutes to about 5 minutes. During this step,the polymer film is deposited on the surface or surfaces of thesubstrate 14 to be coated. Generally, a relatively pinhole-free polymerfilm having a thickness of about 100 Å to about 1000 Å will be depositedon the exposed surface or surfaces. Where a hydrocarbon monomer is usedas the second gas, the polymer film composition should be a hydrocarbonspecies. Here again, after the substrate has been exposed to the plasmafor the desired time period, the power and gas flow are shut off and thechamber 12 is evacuated back to the base pressure.

After the chamber 12 has been stabilized at the base pressure for adesired time period, oxygen is readmitted into the chamber 12 at thesame flow rate and under the same working pressure condition as theprevious steps. The power is again turned on and the substrate isexposed to a second oxygen plasma. Here again, it has been found to bedesirable to expose the substrate with the polymeric film coating to theplasma for a time period in the range of about 5 minutes to about 40minutes, preferably from about 10 minutes to about 20 minutes. Duringthis post-treatment step, it is believe that the polymeric film is mademore amenable to later bonding by the opening of the bonds in thespecies forming the polymeric film and/or by the incorporation of oxygeninto the bonds. For example, where the polymer film is a hydrocarbonspecies, it is believed that the post-treatment step takes away some ofthe hydrogen atoms and opens up some of the bonds in the hydrocarbonlink. After the third step has been completed, the substrate material 14with is polymer film coating can be removed from the chamber 12.

After the polymer film coating has been plasma deposited onto thesurface or surfaces of the substrate material, the coated substratematerial may be laminated to a metallic or non-metallic material notshown. For example, the coated substrate may be laminated to afiberglass/epoxy hardboard or a flexible plastic material such as apolyimide. Any conventional laminating process known in the art,including those that use adhesives, may be used to bond the coatedsubstrate to the metallic or non-metallic material.

To demonstrate the process of the present invention, the following testswere performed.

EXAMPLE I

Samples of wrought copper alloy C11000 foil were first cleaned and thenplaced in a vacuum chamber similar to the one shown in FIGS. 1 and 2.After each sample was placed in the vacuum chamber, the chamber wasevacuated to a background pressure of 10⁻⁵ Torr. Thereafter, oxygen wasintroduced into the chamber at a flow rate of about 5 sccm and at aworking pressure of about 10 millitorr. A power level of about 4.94watts/in² and about 0.88 watts/in³ was applied to the electrodes in thechamber and a plasma was created. The current frequency was at about13.56 MHz. The samples were exposed to this plasma for time periodsranging from about 5 minutes to about 20 minutes.

After the samples were exposed to the oxygen plasma, the chamber wasevacuated and stabilized back to the base pressure. Following this,butadiene was introduced into the chamber at the same flow rate and atthe same working pressure. The same power level and current frequencywere applied and a butadiene plasma was created. The copper foil sampleswere exposed to the butadiene plasma for time periods ranging from about2.5 minutes to about 15 minutes.

Thereafter, the chamber was evacuated and again stabilized back to thebase pressure. Oxygen at the same flow rate and at the same workingpressure as in the other steps was readmitted into the chamber. Power atthe same level and current at the same frequency were applied to theelectrodes to create an oxygen plasma. During this step, the sampleswere exposed to the oxygen plasma for time periods ranging from about 5minutes to about 40 minutes.

Each copper sample treated by this procedure was then laminated to FR-4epoxy preimpregnated fiberglass cloth using the lamination processrecommended by the manufacturer for the manufacture of rigid epoxyprinted circuit boards. After lamination, the degree of adhesion or peelstrength was measured by using a peel test in accordance withappropriate IPC standards. As shown in Table I, the treated coppersamples exhibited peel strength in the range of about 4 to about 8.5lbs/in width.

As a point of comparison, untreated wrought copper alloy C11000 foilsamples were also laminated to FR-4 epoxy preimpregnated fiberglasscloth and subjected to the same peel test. The untreated wrought copperfoils were found to have a peel strength in the order of about 3 toabout 4 lbs/in width.

                  TABLE I                                                         ______________________________________                                        Operational Parameters -                                                                         Power 100 watts                                                               Gas flow 5 sccm                                                               Pressure 10 mtorr                                          Deposition Times (minutes)                                                    Initial  C.sub.4 H.sub.6                                                                           Post-Treatment                                                                            Peel Strength                                O.sub.2  Deposition  O.sub.2     (lb/in width)                                ______________________________________                                        (a)  10      5           20        6.0-8.5                                    (b)   5      5           20        5.0                                        (c)  20      5           20        7.5-8.0                                    (d)  10      2.5         20        6.0                                        (e)  10      10          20        4.0                                        (f)  10      15          20        4.0                                        (g)  10      5           10        7.5-8.0                                    (h)  10      5            5        5.0                                        (i)  10      5           40        5.0                                        ______________________________________                                    

EXAMPLE II

To further demonstrate the present invention, samples of copper alloyC11000 foil were subjected as in Example I to an oxygen plasmapreteatment, a butadiene plasma deposition treatment, and an oxygenplasma post-treatment. The oxygen pretreatment was applied for timeperiods in the range of about 7 minutes to about 10 minutes, thebutadiene plasma deposition treatment was applied for time periods inthe range of about 3.5 to about 5 minutes and the oxygen post-treatmentwas applied for time periods in the range of about 14 minutes to about20 minutes. The gas flow rate and the pressure conditions in each stepwere the same as in Example I. The power level during each step diddiffer from Example I in that it was about 7.4 watts/in² and about 1.33watts/in³.

As in Example I, the treated samples were laminated to FR-4 epoxypreimpregnated fiberglass cloth and subjected to a peel test. As can beseen from Table II, the samples exposed to the butadiene plasmadeposition treatment for a time period of about 3.5 minutes exhibited apeel strength in the range of about 5 to about 6.5 lbs./inch widthwhereas the sample exposed to the butadiene deposition for 5 minutesonly exhibited a peel strength of about 1 lb./inch width. While it isnot clear why the latter sample exhibited a significant loss of peelstrength, the data does suggest that increased power shortens theallowable period for the polymer film deposition step.

                  TABLE II                                                        ______________________________________                                        Operational Conditions -                                                                         Power 150 watts                                                               Gas flow 5 sccm                                                               Pressure 10 mtorr                                          O.sub.2   C.sub.4 H.sub.6                                                                           O.sub.2 Post-                                           Pretreat  Deposition  Treatment Peel Strength                                 (minutes) (minutes)   (minutes) (lb/in width)                                 ______________________________________                                        (a)  10       3.5         14      6.5                                         (b)  7        3.5         20      5.0                                         (c)  7        5.0         14      1.0                                         ______________________________________                                    

While the present invention has been described in terms of a particularplasma deposition equipment, it should be generally applicable to a widerange of such equipment. It is believed, however, that the operationalranges described above for the various processing variables may bestrongly dependent upon the specific geometry of the depositionequipment. Therefore, with a change in equipment, results similar tothose described hereinbefore may be obtained outside the aforementionedprocessing limits.

While particular hydrocarbon monomers have been described to deposit apolymer film, it is believed that similar results would be obtained withvirtually any straight chain hydrocarbon, independent of the C to C bondstructure, i.e. single, double or triple bonds, or chain length.

While the invention has been illustrated in the context of applying ahydrocarbon polymer film to a copper substrate, it is believed thatsimilar polymeric films for improving laminate adhesion could bedeposited on substrates formed from copper alloys, other metals andmetal alloys and non-metallic materials such as silica using the processof the present invention.

While the invention has been described in terms of a batchwisetechnique, the process may also be used in a continuous orsemi-continuous operation. If desired, each step of the three-stepprocess of the present invention could be performed in a separate vacuumchamber. The only limitation to continuous and/or semi-continuousoperations would be not to expose the substrate to be coated to theatmosphere between the various steps of the process. It should berecognized that by performing each step in a separate chamber, it maynot be necessary to evacuate each chamber back to the base pressurebefore subjecting the substrate to the next step of the process.

Depending upon the position of the substrate relative to the electrodes,the polymeric film coating may be deposited on either one surface or aplurality of surfaces of the substrate. If it is desired to deposit thepolymeric coating on only one side while the substrate is in anungrounded condition, two substrates can be placed adjacent one anotherso that the adjacent substrate faces are not coated.

The patents and article set forth in this specification are intended tobe incorporated by reference herein.

It is apparent that there has been provided in accordance with thisinvention a three-step plasma treatment of copper foils to enhance theirlaminate adhesion which fully satisfies the objects, means, andadvantages set forth hereinbefore. While the invention has beendescribed in combination with specific embodiments thereof, it isevident that many alternatives, modificatiohs, and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, it is intended to embrace all suchalternatives, modifications, and variations as fall within the spiritand broad scope of the appended claims.

We claim:
 1. A composite article comprising:a copper or copper alloyfoil having a plasma deposited polymeric film on at least one surface;and a layer of plastic material bonded to said at least one foil surfaceon which said polymeric film is deposited.
 2. The article of claim 1further comprising said plastic material layer being formed from afiberglass epoxy material.
 3. The article of claim 1 further comprisingsaid plastic material layer being formed from a polyimide material. 4.The article of claim 1 further comprising said film having a thicknessin the range of about 100 Å to about 1000 Å.
 5. The article of claim 1wherein said article comprises a printed circuit board.
 6. The articleof claim 1 wherein said article comprises a flexible circuit.
 7. Thearticle of claim 1 further comprising:said polymeric film coated foilexhibiting a peel strength of at least about 4 lbs/in width.
 8. Thearticle of claim 7 further comprising:said polymeric film coated foilexhibiting a peel strength in the range of about 4 lbs/in to about 8.5lbs/in width.
 9. A composite article comprising:a metal or metal alloysubstrate material having a plasma deposited polymeric film on at leastone surface, said film being formed by the process of (a) forming afirst plasma of predominantly oxygen gas in the vicinity of saidsubstrate material; (b) exposing said substrate material to said firstplasma for a first period of time; (c) forming a plasma of a hydrocarbonmonomer gas in the vicinity of said substrate material; (d) exposingsaid substrate material to said hydrocarbon monomer gas plasma for asecond period of time; (e) forming a second plasma of predominantlyoxygen gas in the vicinity of said substrate material; and (f) exposingsaid substrate material to said second oxygen plasma for a third periodof time; and a layer of plastic material bonded to said at least onesurface.
 10. The article of claim 9 further comprising:said substratematerial being formed from copper or a copper base alloy.